(1) Field of the Invention
The present invention relates to a femtosecond laser device with stabilized output, in particular to a device and method relating to output stabilization by a regenerative amplifier.
(2) Description of the Related Art
Femtosecond lasers, so-called because they issue laser beams with pulse widths of femtosecond order, have a small pulse width and a very high energy density. For this reason, they are often used for machining applications, due to advantages such as having no thermal effects in the periphery of the portion being machined and the lack of debris due to its vaporization.
Therefore, femtosecond lasers have often been used in machining devices in recent years, and equipment has become available for this purpose.
However, prolonged use causes parameters of the laser device such as LD current, Pockels cell voltage and optical axis of the seed beam to deviate from their optimal values, so that the target output can no longer be obtained.
Since the gain of regenerative amplifiers was not able to be changed in conventional femtosecond lasers, the output depended on the pump beam. Additionally, the output level of the pump beam varies due to temporal changes. Hence, the drive current of the pump laser must be frequently adjusted to maintain the output of a femtosecond laser at its original level. Furthermore, changes in the properties of the optical materials used in regenerative amplifiers such as damage, temporal changes and temperature changes can make it impossible to maintain the output level of regenerative amplifiers simply by raising the output of the pump laser. Additionally, if an attempt is made to compensate for a large decrease in the gain of a regenerative amplifier by raising the output of the pump laser, this can overload the regenerative amplifier and cause damage. Additionally, this causes deterioration to advance more quickly.